Yes, the white dust is aluminium oxide. It's not pretty but my understanding is that it's generally not as harmful as rust is to steel. That's because the oxide tends to form a stable layer which protects the underlying metal whereas rust tends to come away and expose the underlying metal. In fact if you have alloy wheels and other parts they are usually protected by anodizing, which is a method for increasing the thickness of the oxide layer.

With any frame, once it reaches the point where it's looking too shabby or you are concerned about rust or oxide damage, you can get them re-enameled or powder coated. A friend of mine had nothing but praise for the work done by Colour-Tech on his frame, for those of you in the UK. Have a look at their gallery - they've done some lovely work and they aren't expensive.

John